Electric siren



Jan. 19, 1937. c. P. MEUSSDORFFER 2,068,427

ELECTRIC S IREN Filed July 22, 1950 INVENTOR.

ATTORNEYS;

Patented Jan. 19 1937 UNITED STATES PATENT OFFICE 2 Claims.

This invention relates to electric sirens and has for its objects an improvement in such sirens of the electric motor driven type whereby the usual clutch may be disposed with and the armature will be free running without impediment of dragging brushes, and which will provide for control of the siren through a relay switch so that the heavy operating current need be wired only in a direct short path from the battery or other source of current to the siren. Other features and objects of the invention will appear in the following specification and accompanying drawing.

In the drawing Fig. 1 is a side elevation of my improved electric siren with portion shown in section.

Fig. 2 is a top plan view of the siren of Fig. 1.

Fig. 3 is an end view of the motor of the siren.

Fig. 4 is a cross section of the motor taken through the line 4-4 of Fig. 2 showing in diagrammatic. form the wiring and control switch.

Fig. 5 is a diagrammatic end view of the motor showing a form of the brush control mechanism wherein four brushes are used instead of two.

Before describing my invention it would be well to state that in electric sirens as used on police cars, fire trucks, etc., it is desirable that the rotor spin freely after opening the motor energizing switch so as to continue the note and give the characteristic sound, and therefore it is the practice to incorporate an automatic clutch which will disconnect the siren rotor from the motor shaft. In such cases, however, every time the switch is closed the motor armature itself being usually at rest draws unduly on the battery with a consequence that it is short lived.

In my construction I dispense entirely with a clutch to release and engage the siren rotor, have it permanently secured to theshaft of the motor armature and simply lift the brushes from the armature automatically when the control switch is open, thus providing a free running siren free from drag of armature brushes, of longer free running on account of the weight and momentum of the motor armature which adds to the weight of the loaded rotor of the siren since they are secured to the same shaft.

Besides the above, even when the siren has slowed down below an audible note the armature is nevertheless in motion and consequently upon closing the switch no great drain on the battery takes place.

The brushes are pulled down upon the commutator by a solenoid energized by a distant control switch and hence functions as a relay switch thus avoiding wiring the heavy motor current through the control switch.

Since the brushes are lifted from the commu- 5 tator while same is at high speed with a minimum current passing, no inj us arcing takes place, and the brushes being in actual contact with the commutator during a short interval for each note their life is much increased. 10

In the drawing I is the motor base, 2 the motor body inclosing the field coils and armature not seen, 3 the shaft of the armature supported in ball bearings one of which is seen at 4. The forward end of the shaft is preferably tapered as shown at 5 and clamped to the hub 6 of a massive metal rotor l having a peripheral flange 8 of reduced thickness apertured around its circumference as at 9 in the well known way to emit a note when passing similar apertures it] in a V casing or stator ll which is made of sheet metal and partially surrounds the rotor so that the air is drawn inwardly in the center of the rotor for ejection from the peripheral openings.

A feature of the rotor is the heavy annular flange or ring '1 at the outer end of the rotor, and the double walls l2, l3 of the sheet metal stator which are bowed apart as shown, secured at their inner margins to the motor body, part l2 flanged outwardly at I4 and part [3 turned tightly into the corner and welded to part H at l5. Part [4 is also welded, soldered or otherwise secured to part II, though if desired parts i l and H may be one continuous deep drawing without affecting the advantages of the double-walled construction as shown at [2 and I3.

The rear bearing of the shaft is carried in flange H5 at the end of which is a removable plate I! and through which flange and plate rotatably extend a pair of small shafts E8 on the inner ends of which are mounted the motor brushes l9 in a manner so that by turning the shafts the brushes may be swung against or away from the commutator 2|. The brushes may be independently adjusted on their shafts by means of set screws 22, and adjustably clamped to the outer ends of the shafts are arms 23 directed toward one another and both pivotally yoked together by a block or equalizer 24 in turn connected by a tension spring 25 to one arm of a bell crank 26 pivoted to a bracket 21 carried by the motor frame, while the other arm of the bell crank is pivotally connected at 28 to one end of a link 29 pivoted at its other end at 30 to the end of a solenoid core 3| slidable within a coil 32 housed within a bore in the motor base.

The solenoid core carries a disk armature 33 which when the core retracts into the coil is attracted by a circular pole piece 34 projecting from the coil housing but is prevented from direct contact therewith by means of a small nonmagnetic disk 35 secured to the inner end of the core 3| and adapted to limit the travel of the core by striking a fixed pole piece 36 secured within the coil adjacent its inner end.

A spiral spring 31 surrounding the core piece and bearing against the armature 33 normally forces the core outward to lift the upper arm of bell-crank 26 and by means of a small plunger 38 positioned within spring 25 and pivoted at one end to the bell-crank forces the yoke 24 upward to thereby turn shafts I8 and lift both brushes from the commutator. A small bumper spring 39 or other resilient device limits the travel of the solenoid without shock in releasing the brushes.

When the solenoid core is drawn inward by energizing of its coils the bell-crank 26 tensions spring 25 pulling yoke 24 downwardly and resiliently clamping both brushes against the armature. The bell-crank is shown pierced with several holes for adjusting the connections to take care of wear on the brushes, and the yoke plate is shown with an extra hole 40 offset further from the center line of the plate than the hole in which spring 25 is hooked so that when the brushes are new and long this plate may be turned upside down and the spring will then be under about the same tension as shown in the drawing, and since the brushes and arms 23 are all adjustable on the shaits I8 it will be seen that the brushes may be adjusted for any degree-of pressure desired.

In Fig. 4 it will be seen that the motor is heavily wired from the battery to one pole and the other grounded and that a small control circuit runs from the battery to a control switch A in series with the solenoid coil 32 also grounded at the other terminal. The control switch A is placed at any convenient position on the vehicle on which the siren is installed.

In operation, when the switch is closed, the solenoid is energized and core drawn in putting tension on spring 25 and pulling both brushes tightly against the commutator thus completing the motor circuit, and upon opening the switch spring 31 reve .es the action and throws ofl the brushes permitting siren to spin freely under combined momentum of motor armature and siren rotor.

In Fig. 5 a brush control mechanism for four brushes is diagrammatically shown.

In this form, all four brushes have a. common control means similar to bell crank 26, and spring and plunger linkage 25, 38 as shown in the previously described form. The individual brushes are mounted on shafts IS in the same manner as shown in Fig. 4, which shafts rotatably extend through removable end plate H. To the outer ends of shafts iii are secured arms 45 extending substantially perpendicular away from each other. Hub 45 projecting outwardly from the center of end plate I! revolvably carries a disk 41, said disk being provided with an arm 48 extending therefrom for revolving the disk on hub 46.

The free end of arm 48 is connected to the solenoid as shown in Figs. 1 to 4 through linkage 25, 38, 26 and 29.

The free ends of brush arms 45 are connected to the margin of disk 41 at spaced intervals therearound by coil springs 50, so that upon rotation of disk 41 in the direction indicated by the arrow through means of arm 48, springs 50 will be tensioned, the brush arms 45 will be pulled toward the disk and the brushes will be brought in close contact with the commutator.

Within each of coil springs 50 is a small plunger 5| which forces arms 45 back into neutral position with brushes out of contact with commutator when the main switch is opened and the tension of the springs is relieved.

In the arrangement shown in Fig. 5, as the brushes are worn away, the coil springs 50 permit eifective contact of all brushes with the commutator regardless of uneven wear of one or more of the brushes, but in order to avoid excessive wearing away of the brushes I provide a stop or projection 52 which extends from the edge of the disk 41 and which is adapted to engage against a stop pin 53 projecting from plate l1 so as to limit the movement of the brushes against the commutator at a point where one or more of the brushes should be replaced.

Having thus described my invention it will be evident to any mechanic that variations in detail may be made without departing from the spirit of the invention, and as may fall within the scope of the appended claims.

I claim:

1. In an electric siren, a rotor, an electric motor in an electrical circuit, said electric motor including an armature, a commutator and brushes thereon, a single shaft to which the rotor and armature are fixedly secured for rotation to gether, means mounting the shaft for rotation, means for lifting the brushes off the commutator when the electrical circuit is broken, means for lowering the brushes onto the commutator when the electrical circuit is closed, and a switch in the electrical circuit for opening and closing the circuit.

2. In an electric siren, a rotatably mounted rotor, an electric motor in an electrical circuit arranged for driving said rotor, said motor including a rotatably mounted armature, a commutator and brushes thereon, means mounting said brushes for movement toward and away from the commutator, means positively connecting said 1 rotor and armature for rotation together at all times, means connected to said brushes arranged and adapted to press said brushes tightly against the commutator when the electrical circuit is closed and to release the pressure of the brushes against the commutator when the electrical circuit is broken whereby the armature will function as a flywheel substantially free of frictional resistance by the brushes when the circuit is broken, a switch in the electrical circuit for opening and closing the circuit.

CONRAD P. IVIEUSSDORFFER. 

